PROPAGULES AND OFFSPRING
Patterns of Development Nutritional mode 1) Planktotrophy - larval stage feeds This separates marine invertebrates from all others – can feed in dispersing medium - Probably most primitive
Patterns of Development Nutritional mode 2) Maternally derived nutrition a) Lecithotrophy - yolk b) Adelphophagy – feed on eggs or siblings c) Translocation – nutrient directly from parent
Patterns of Development Nutritional mode 3) Osmotrophy - Take DOM directly from sea water
Patterns of Development Nutritional mode 4) Autotrophy - by larvae or photosynthetic symbionts - In corals, C 14 taken up by planulae - In Porites, symbiotic algae to egg
Patterns of Development Site of Development 1) Planktonic development - Demersal – close to seafloor - Planktonic – in water column 2) Benthic development - Aparental – independent of parent – encapsulation of embryo - Parental – brooding – can be internal or external
Patterns of Development Dispersal Potential of Larvae 1) Teleplanic - Larval period – 2 months to 1 year + 3) Anchioplanic - larval period – hours to a few days 2) Achaeoplanic – coastal larvae -1 week to < 2 months (70% of littoral species)
Developmental Patterns -Kinds of eggs Isolecithal Telolecithal Cleavage through entire egg Cleavage not through entire egg Holoblastic Meroblastic 1) Fertilization patterns 2) Development patterns 3) Dispersal patterns 4) Settlement patterns
Developmental Patterns -Kinds of eggs Isolecithal - HoloblasticTelolecithal - Meroblastic 1) Fertilization patterns 2) Development patterns 3) Dispersal patterns 4) Settlement patterns
Developmental Patterns -Kinds of eggs Isolecithal Telolecithal Holoblastic Meroblastic Planktotrophic larvae Lecithotrophic larvae 1) Fertilization patterns 2) Development patterns 3) Dispersal patterns 4) Settlement patterns
LIFE HISTORY TRAITS Fecundity - Total number of offspring (expressed as a number of offspring over a period of time) Three categories of fecundity 1) Potential – number of oocytes in ovary 2) Realized – number of eggs produced 3) Actual – number of hatched larvae CENTRAL TO THIS – FECUNDITY – EXPENSIVE AND DIRECTLY LINKED TO FITNESS
Relationship of fecundity to other traits 1)Egg size - Generally egg size 1/fecundity Look at poeciliogonous species Streblospio benedicti Produce both lecithotrophic and planktotrophic larvae Lecithotrophic – egg 6X larger Planktotrophic –6X as many eggs Same reproductive investment
OFFSPRING SIZE -volume of a propagule once it has become independent of maternal nutrition Egg size – most important attribute in: 1) Reproductive energetics 2) Patterns of development and larval biology 3) Dispersal potential
Effects of Offspring Size 1) Fertilization -some controversy about evolution of egg size Either a) influenced by prezygotic selection for fertilization OR b) post-zygotic selection
Effects of Offspring Size 1) Fertilization One consequence of size-dependent fertilization Low sperm concentration larger zygotes High sperm concentration smaller zygotes (effects of polyspermy) Size distribution of zygotes - function of both maternal investment and of local sperm concentration
Effects of Offspring Size 2) Development Prefeeding period increases with offspring size Feeding period decreases with offspring size
Effects of Offspring Size 2) Development Prefeeding period increases with offspring size Feeding period decreases with offspring size Evidence? Planktotrophs 1)pre-feeding period -larger eggs take longer to hatch in copepods - in nudibranchs – no effect
2) Entire planktonic period -review of 50+ echinoids – feeding 5 echinoids – non feeding Larval period decreases with increase in egg size But for polychaetes and nudibranchs Dev. time Egg size ( m) NudibranchsPolychaetes Planktotrophic Lecithototrophic
Intraspecific comparisons Larger larvae result in longer lifetimes e. Ascidians and urchins Dev. time Egg size ( m)
POST -METAMORPHOSIS Does egg size affect juvenile size? Echinoids Nudibranchs Conus a.Planktotrophs Size at metamorphosis is independent of egg size b. Non-feeding larvae H. erythrogramma -used for post-metamorphic survival -most maternal investment (lipid) -not necessary for larval development
POST -METAMORPHOSIS Does egg size affect juvenile size? b. Non-feeding larvae Bugula -larval size affects - post settlement mortality - growth -reproduction -offspring quality -need energy to develop feeding structures – 10 – 60% of reserves
Summary of Offspring Size Predictions -closer to metabolic minimum 1)Species with non-feeding larvae -greatest effect is on post-metamorphic survival 2) Sources of mortality - physical, disturbance, stress – size independent - biological sources – size dependent 3) Offspring size - very different effects among populations
SOURCES OF VARIATION IN OFFSPRING SIZE 1) Offspring size varies a) within broods b) among mothers c) among populatioins 2) Within populations a) stress – salinity, temperature, food availability, pollution b) maternal size - +ve correlation
3) Among populations a) habitat quality – poorer habitat results in smaller offspring b) latitudinal variation Bouchard & Aiken 2012
3) Among populations a) habitat quality – poorer habitat results in smaller offspring b) latitudinal variation Bouchard & Aiken 2012
OFFSPRING SIZE MODELS Same basic features 1) Trade off in size and number of offspring 2) Offspring size-fitness function 1) Trade off in size and number of offspring N =c/S c = resources N = number S = Size Refers to energetic costs to mother not energy content of eggs Size:energy content more variable
OFFSPRING SIZE MODELS Same basic features 1) Trade off in size and number of offspring 2) Offspring size-fitness function 1) Trade off in size and number of offspring -other costs may be involved e.g. packaging of embryos e.g. brood capacity of the mother
OFFSPRING SIZE MODELS Same basic features 1) Trade off in size and number of offspring 2) Offspring size-fitness function - Focused on planktonic survival Decrease in size Longer planktonic period Higher mortality
OFFSPRING SIZE MODELS Same basic features 1) Trade off in size and number of offspring 2) Offspring size-fitness function Other effects- fertilization rates - facultative feeding - generation time - post metamorphic effects VARIATION IN OFFSPRING SIZE AFFECTS EVERY LIFE HISTORY STAGE
SUMMARY OF EFFECTS Planktotrophs - Strong effects of offspring size on life history stages 1) Fertilization in free (broadcast) spawners 2) Larger eggs result in larvae that spend less time in the plankton 3) Larger larvae feed better
VARIATION IN OFFSPRING SIZE AFFECTS EVERY LIFE HISTORY STAGE SUMMARY OF EFFECTS 2. Non-feeders - Strong effects of offspring size on life history stages 1) Fertilization success 2) Developmental time 3) Maximize larval lifespan 4) Postmetamorphic performance 5) Subsequent reproduction and offspring size
VARIATION IN OFFSPRING SIZE AFFECTS EVERY LIFE HISTORY STAGE SUMMARY OF EFFECTS 3. Direct developers - Strongest effects of offspring size on life history stages - Mothers may be able to adjust provisioning to local conditions